1. Electricity
Chapter 14

2. Section 2 Electric Charge and Static Electricity
Chapter 14
Objectives
Explain the role of charged particles in atoms and in charged objects.
Describe how electric force depends on charge and distance.
Describe three ways in which an object can become charged.
Compare conductors with insulators.
Give two examples of static electricity and electric discharge.

3. Chapter 14 Electric Charge
Section 2 Electric Charge and Static Electricity
Chapter 14
Electric Charge
Charges And Forces Atoms are composed of particles with electric charge.
The law of electric charges states that like charges repel and opposite charges attract.
When you rub you hair on a balloon, why will it stick to the wall?
Imbalance of charges
Hair becomes negative (more electrons)
Balloon becomes positive (fewer electrons)

4. Chapter 14 The Structure of an Atom
Section 2 Electric Charge and Static Electricity
Chapter 14
The Structure of an Atom

5. Size of the Charges
The unit of measure for electrical charge is the Coulomb
Electrons and Protons have the same charge, but opposite
Electrons have a charge of -1.6x10-19C
Protons have a charge of +1.6x10-19C

6. Electric Charge, continued
Section 2 Electric Charge and Static Electricity
Chapter 14
Electric Charge, continued
The Force Between Protons and Electrons Because protons and electrons have opposite charges, they are attracted to each other.
The Electric Force and the Electric Field The force between charged objects is an electric force. An electric field is the region around a charged object in which an electric force is exerted on another charged object.

7. Chapter 14 The Law of Electric Charges
Section 2 Electric Charge and Static Electricity
Chapter 14
The Law of Electric Charges

8. Section 2 Electric Charge and Static Electricity
Chapter 14
Charge It!
Friction Charging by friction happens when electrons are “wiped” from one object onto another.
Like a balloon through your hair
Conduction Charging by conduction happens when electrons move from one object to another by direct contact.
Like touching the handle of a door after shuffling your feed
Induction Charging by induction happens when charges in an uncharged metal object are rearranged without direct contact with a charged object.

9. Section 2 Electric Charge and Static Electricity
Chapter 14

10. Chapter 14 Charge It!, continued
Section 2 Electric Charge and Static Electricity
Chapter 14
Charge It!, continued
Conservation of Charge When you charge something by any method, no charges are created or destroyed. The numbers of electrons and protons stay the same.
Detecting Charge You can use a device called an electroscope to see if something is charged.

11. Chapter 14 Charging by Contact
Section 2 Electric Charge and Static Electricity
Chapter 14
Charging by Contact

12. Chapter 14 Moving Charges
Section 2 Electric Charge and Static Electricity
Chapter 14
Moving Charges
Conductors An electrical conductor is a material in which charges can move easily.
Silver, gold, copper are best
Most other metals
Insulators An electrical insulator is a material in which charges cannot move easily
Air, cloth, paper, plastic, wood.

13. Chapter 14 Static Electricity
Section 2 Electric Charge and Static Electricity
Chapter 14
Static Electricity
Static electricity is the electric charge at rest on an object.
Electric Discharge The loss of static electricity as charges move off an object is called electric discharge. One of the most dramatic examples of electric discharge is lightning. The next slide shows how lightning is formed.

14. Chapter 14 How Lightning Forms
Section 2 Electric Charge and Static Electricity
Chapter 14
How Lightning Forms

15. Static Electricity, continued
Section 2 Electric Charge and Static Electricity
Chapter 14
Static Electricity, continued
Lightning Dangers It is particularly dangerous to be at the beach or on a golf course during a lightning storm. Even standing under a tree during a storm is dangerous.
Lightning Rods A lightning rod is a pointed rod connected to the ground by a wire. Objects that are joined to Earth by a conductor, such as a wire, are grounded.

16. Electric Force
The attraction of a positively charged particle to a negatively charged particle
Electric force is proportional to charge and distance
Force is equal to the product of the charges (Fe=CaCb)
Force is inversely proportional to the SQUARE of the distance
Fe=1/(da-db)2
If you double the distance, the force is one-fourth
If you half the distance, the force is 4 times

17. Electric Force Electric Force acts in a ‘Field’
Electric Field is the area in which the oppositely charged items attract each other

18. Section 3 Electric Current and Electrical Energy
Chapter 14
Bellringer
What is the difference between something that is direct and something that is alternating? How does the difference relate to electric current?
Record your response in your science journal.

19. Chapter 14 Objectives Describe electric current.
Section 3 Electric Current and Electrical Energy
Chapter 14
Objectives
Describe electric current.
Describe voltage and its relationship to electric current.
Describe resistance and its relationship to electric current.
Explain how a cell generates electrical energy.
Describe how thermocouples and photocells generate electrical energy.

20. Chapter 14 Electric Current
Section 3 Electric Current and Electrical Energy
Chapter 14
Electric Current
Electric current is the rate at which charges pass through a given point. Electric current is expressed in units called amperes, or amps.
Making Charges Move When you flip a switch, an electric field is set up in the wire at the speed of light. The electric field causes the free electrons in the wire to move.

21. Electric Current, continued
Section 3 Electric Current and Electrical Energy
Chapter 14
Electric Current, continued
Commanding Electrons to Move This electric field is created so quickly that all electrons start moving through the wire at the same instant. Think of the electric field as a command to the electrons to charge ahead.

22. Electric Current, continued
Section 3 Electric Current and Electrical Energy
Chapter 14
Electric Current, continued
Alternating Current and Direct Current There are two kinds of electric current—direct current (DC) and alternating current (AC).

23. Section 3 Electric Current and Electrical Energy
Chapter 14
Voltage
Voltage is the potential difference between two points in a circuit. Voltage is expressed in volts (V).
Voltage and Energy Voltage is a measure of how much work is needed to move a charge between two points.You can think of voltage as the amount of energy released as a charge moves between two points in the path of a current.

24. Chapter 14 Voltage, continued
Section 3 Electric Current and Electrical Energy
Chapter 14
Voltage, continued
Voltage and Electric Current As long as there is a voltage between two points on a wire, charges will flow in the wire. The size of the current depends on the voltage.
Varying Nature of Voltage Different devices need different levels of voltage.

25. Section 3 Electric Current and Electrical Energy
Chapter 14
Resistance
Resistance is the opposition to the flow of electric charge.
Resistance and Material Good conductors, such as copper, have low resistance. Poor conductors, such as iron, have higher resistance.
Resistance, Thickness, and Length Thick, short wires have less resistance than thin, long wires.

26. Chapter 14 Resistance, continued
Section 3 Electric Current and Electrical Energy
Chapter 14
Resistance, continued
Resistance and Temperature In general, the resistance of metals increases as temperature rises.

27. Factors That Affect Resistance
Section 3 Electric Current and Electrical Energy
Chapter 14
Factors That Affect Resistance

28. Generating Electrical Energy
Section 3 Electric Current and Electrical Energy
Chapter 14
Generating Electrical Energy
Cells change chemical or radiant energy into electrical energy.
Parts of a Cell A cell contains a mixture of chemicals called an electrolyte. Every cell also has a pair of electrodes made from conducting materials.
Kinds of Cells Two kinds of cells are wet cells and dry cells. The electrolytes in dry cells are solid or pastelike.

29. Chapter 14 How a Cell Produces an Electric Current
Section 3 Electric Current and Electrical Energy
Chapter 14
How a Cell Produces an Electric Current

30. Generating Electrical Energy, continued
Section 3 Electric Current and Electrical Energy
Chapter 14
Generating Electrical Energy, continued
Thermocouples Thermal energy can be converted into electrical energy by a thermocouple.
Photocells A photocell converts light energy into electrical energy.

31. Chapter 14 Concept Mapping
Magnetism and Electricity
Concept Mapping
Use the terms below to complete the concept map on the next slide.
electric current
battery
charges
thermocouple
photocell
cell

32. Chapter 14
Magnetism and Electricity

33. Chapter 14
Magnetism and Electricity

34. End of Chapter 14 Show Chapter menu Resources
Copyright © by Holt, Rinehart and Winston. All rights reserved.

35. Chapter 14
Standardized Test Preparation
FCAT
For the following questions, write your answers on a separate sheet of paper.

36. Chapter 14
Standardized Test Preparation
1. Charged particles in solar wind bombard Earth constantly. The image below shows how the paths of these charged particles are bent as they approach Earth. What causes the charged particles in the solar wind to change course as they approach Earth?
A. Earth’s gravity
B. Earth’s radiation
C. Earth’s electric field
D. Earth’s magnetic field

37. Chapter 14
Standardized Test Preparation
1. Charged particles in solar wind bombard Earth constantly. The image below shows how the paths of these charged particles are bent as they approach Earth. What causes the charged particles in the solar wind to change course as they approach Earth?
A. Earth’s gravity
B. Earth’s radiation
C. Earth’s electric field
D. Earth’s magnetic field

38. Chapter 14
Standardized Test Preparation
2. Several forces act on the objects in the image below. One force pushes the objects apart. Another force pulls the object together. What force pulls the two objects toward each other?
F. gravity
G. convection
H. electric force
I. magnetic force

39. Chapter 14
Standardized Test Preparation
2. Several forces act on the objects in the image below. One force pushes the objects apart. Another force pulls the object together. What force pulls the two objects toward each other?
F. gravity
G. convection
H. electric force
I. magnetic force

40. Chapter 14
Standardized Test Preparation
3. After sliding down a plastic slide, Juan notices the hairs on his arm are standing on end. Which of the following forces pushes the hairs up?
A. atomic force
B. electric force
C. magnetic force
D. gravitational force

41. Chapter 14
Standardized Test Preparation
3. After sliding down a plastic slide, Juan notices the hairs on his arm are standing on end. Which of the following forces pushes the hairs up?
A. atomic force
B. electric force
C. magnetic force
D. gravitational force

42. Chapter 14
Standardized Test Preparation
4. George wants to generate electrical energy in his house from a renewable resource. What device from the following choices could he use as a model?
F. a nuclear power plant
G. a coal fired power plant
H. a diesel electric generator
I. a solar roadside emergency phone

43. Chapter 14
Standardized Test Preparation
4. George wants to generate electrical energy in his house from a renewable resource. What device from the following choices could he use as a model?
F. a nuclear power plant
G. a coal fired power plant
H. a diesel electric generator
I. a solar roadside emergency phone

44. Chapter 14
Standardized Test Preparation
5. The sketch below shows a diagram of Angelica’s experiment. Angelica placed the “black box” in a hot attic during the day and observed the light bulb shining brightly. During the night, the light bulb went out.
Part A Identify the type of energy going into the light bulb that was generated by this system.
Part B Explain why the light bulb went out at night.

45. Chapter 14
Standardized Test Preparation
5. Part A Identify the type of energy going into the light bulb that was generated by this system.
Part A: Full-credit answers should include the following points: light bulbs are powered by electrical energy; the black box in the attic must generate electrical energy; the black box generates electrical energy from the thermal energy in the hot attic.
Part B Explain why the light bulb went out at night.
Part B: Full-credit answers should include the following points: at night, the sun does not warm up the attic; there is not enough thermal energy in the attic at night for the black box to generate the electrical energy required to illuminate the light bulb.

46. Chapter 14
Section 1 Magnets and Magnetism

47. Chapter 14
Section 1 Magnets and Magnetism

48. Chapter 14
Section 1 Magnets and Magnetism

49. Chapter 14
Section 1 Magnets and Magnetism

50. Chapter 14
Section 1 Magnets and Magnetism

51. Chapter 14 The Structure of an Atom
Section 2 Electric Charge and Static Electricity
Chapter 14
The Structure of an Atom

52. Chapter 14 The Law of Electric Charges
Section 2 Electric Charge and Static Electricity
Chapter 14
The Law of Electric Charges

53. Section 2 Electric Charge and Static Electricity
Chapter 14

54. Section 2 Electric Charge and Static Electricity
Chapter 14

55. Chapter 14 How Lightning Forms
Section 2 Electric Charge and Static Electricity
Chapter 14
How Lightning Forms

56. Section 3 Electric Current and Electrical Energy
Chapter 14

57. Section 3 Electric Current and Electrical Energy
Chapter 14

58. Section 3 Electric Current and Electrical Energy
Chapter 14

59. Section 3 Electric Current and Electrical Energy
Chapter 14

60. Chapter 14 How a Cell Produces an Electric Current
Section 3 Electric Current and Electrical Energy
Chapter 14
How a Cell Produces an Electric Current

61. Section 3 Electric Current and Electrical Energy
Chapter 14

62. Chapter 14
Standardized Test Preparation

63. Chapter 14
Standardized Test Preparation

64. Chapter 14
Standardized Test Preparation